The present invention relates to a method for protecting a tuyere assembly and a refractory lining of a furnace.
The interior of a shaft furnace, such as a blast furnace, is generally lined with a refractory material. The latter usually consists of items such as bricks or blocks, e.g. made from carbon, aluminium silicate or ceramic material, which are cemented for imperviousness and stability. Usually, different types of bricks or blocks are used in different zones, according to the predominant type of stress in the respective zone.
It is well known in the art that the refractory lining is subject to expansion. Basically two different effects can cause refractory lining expansion. A first effect is thermal expansion caused by the temperature increase of the refractory lining during start-up of the blast furnace. Thermal expansion is generally reversible. A second effect is referred to as “chemical expansion”. This effect is due to chemical reactions that take place in the refractory material during its lifetime. Such chemical reactions cause an irreversible expansion of the refractory lining.
It will be noted that the refractory lining can find external bodies on the way of its expansion displacement. Such a situation occurs with the plurality of circumferentially arranged tuyere assemblies, which penetrate through the refractory lining into the blast furnace. As the refractory lining surrounds each of these tuyere assemblies, the latter can be on the way of the expansion of the wall lining. This can result in deformation of the tuyere assemblies and/or in a crushing of the expanding refractory lining under the tuyere assemblies.
To prevent unnecessary downtime and damage, it is important to take preventive measures. A known approach is to provide softening layers between refractory items, which compensate for dilatation of the refractory lining. They generally consist of thin, compressible and isolating joint plates. U.S. Pat. No. 3,805,466 describes such an approach. However, for stability and other reasons, the height of such known softening layers is limited. Thus, the summed vertical dimension of such layers is generally in the order of tenths of a percent of the summed vertical refractory lining dimension from furnace foundation to the tuyere assembly. Such layers can, at least partly, compensate for thermal expansion or dilatation of the refractory lining. However, they can normally not compensate for chemical expansion of the refractory lining. Indeed, chemical expansion is variable, generally irreversible and difficult, if not impossible, to predict. Moreover, chemical expansion is progressing over refractory lining service-life. With increasing extent of chemical expansion, the capability of the abovementioned layers to compensate for dilatation is reduced. Consequently, damage to the tuyere assemblies and/or the refractory lining cannot be efficiently prevented by known softening layers.